This invention relates in general to rollers and more particularly to a roller for supporting a rotating drum and to a process for manufacturing such a roller.
The typical household clothes drier has a cabinet, a drum which revolves in the cabinet about a horizontal axis, and some type of arrangement for heating air and forcing that air through the drum. One end of the drum is open so that wet clothes may be placed in the drum, and of course when the drum turns, the clothes tumble in a constant stream of warm air which extracts moisture from the clothes. Since one end of the drum must be left open to place clothes in and withdraw them from the interior of the drum, the drum is not supported, at least at that end, along its axis of rotation. On the contrary, the open end of the drum rotates on small support rollers which lie beneath the drum and form a cradle for the rotating drum.
The rollers of course must be strong enough to support the weight of the drum as well as the weight of wet clothes within the drum, and they further must run smoothly along the exterior cylindrical surface of the drum without producing excessive noise. In addition, they must be durable. To this end, the conventional support roller includes a molded plastic hub, a metal sleeve bearing set into the hub, and a rubber tire around the hub. The tire of course provides the silence which is so desirable. In the manufacture of such a roller, the rubber tire is normally molded apart from the hub and then fitted snugly into die configured to produce the wheel. Then the plastic is injected into the die where it conforms not only to the die surfaces, but also to those surfaces of the tire that are presented inwardly toward the axis of rotation for the roller. As the polymer material cools it undergoes a slight contraction, and this of course tends to loosen the fit between the wheel and tire. When the roller is placed in operation, the fit loosens still further, for the rubber of the tire is stressed on a cyclical basis, or is in other words kneaded, and this tends to elongate the rubber tire. A loose tire may slip with respect to the molded plastic hub, which tends to cause even greater elongation, and furthermore a loose tire will not carry substantial lateral loads. Thus, the chances of a loose tire working off of its hub are much greater than the possibility of a tight or intimately fitted tire doing so.
Heretofore attempts have been made to retain the tire on the hub by providing positive interlocks betwee the tire and hub. For example the tire may be provided with lugs on its inwardly presented surface, and these lugs embed within the plastic of the hub when the hub is molded. However, the lugs also produce variations in the thickness in the tire, and these variations set up stress concentrations when the support roller is in operation. The stress concentrations in turn shorten the life of the tire.